Why is there intro/outro silence in songs?

I agree with Akira. On a lot of albums, tracks blend into one another because the songs are linked thematically. Conversely, a few seconds of silence in the beginning and end can help to establish a track as its own statement or idea. Also, since most albums have songs written in a variety of keys, the silence can help smooth the transition between songs in distant keys by cleansing your ears, so to speak, of the key of the previous song.

But the silence can definitely be a pain when making a mix CD or something like that. I was toying with the idea of making a CD for the GFF CD exchange, and one track I was thinking about using had about eight seconds of silence at the end of it that killed the momentum I was trying to build.

Jam it back in, in the dark.